Heart disease is known as the leading cause of death in the United States. The National Center for Health Statistics reported over 2.4 million deaths in the US in the year 2001, with heart disease being the leading cause with 700,142 cases. This accounts for 38.5% of all deaths in the United States in that year. According to the National Institutes of Health, heart disease is also the leading chronic preventable disease in the US today, outpacing all other preventable conditions. In statistical terms, the number of US cases affected by heart disease is 64,400,000, or 22.6% of the US population, with an associated cost of the disease for 2004 exceeding $368.4 billion.
Heart disease is defined as any disorder that affects the heart's ability to function properly, and is most commonly caused by narrowing or blockage of the coronary arteries, which supply blood to the heart itself. The treatment for coronary artery disease is mainly by angioplasty and surgical revascularization, known as coronary artery bypass graft (CABG). Due to the nature of the disease, CABG has become one of the most commonly performed procedures in the world. According to the American Heart Association's Heart Disease and Stroke statistics, 467,000 CABG surgeries comprising 346,000 men and 121,000 women were performed in the United States in 2003. This number increased to about 600,000 cases in 2005.
During a CABG surgery, vessels are connected to the heart to bypass the coronary artery blockages. Of those vessels, or conduits, the internal mammary artery (IMA) is the primary and the most preferred by surgeons for the bypass procedure. The IMA is harvested from the chest wall near the sternum and attached to the heart to supply blood to the area supplied by the blocked vessel experiencing hypo-perfusion.
The IMA (also known as the internal thoracic artery or ITA) is a major conduit for use in coronary artery bypass graft. The IMA is located on the interior surface of the chest on each side starting from the neck down, originating at the subclavian artery and ending at the superior epigastric artery. The IMA supplies blood to the chest wall including the ribs, sternum and breasts.
The mammary artery is an important conduit for bypass surgery as it is an artery rather than a vein; accordingly it has the lowest risk of thrombosis and occlusion among all other conduits. Consequently the state of the mammary artery has important prognostic value, and a well harvested and good flowing mammary artery determines the successful outcome of the surgery.
One of the reasons the IMA is a preferred conduit for CABG is due to its special properties and characteristics that differentiates it from other vessels. For example, in the inner layer of the IMA, the endothelium is thicker in this artery compared to other arteries; therefore, this vessel is rich in endothelial cells. Endothelial cells are responsible for the arterial features of a vessel, being active in production of multiple substances that actively mediate the arterial wall activity and maintenance of the vessels integrity. Due to these specific properties, the mammary artery has the best outcome as a graft in CABG. These outcomes are translated as the patency rate of 90% in 10 years when a mammary artery is used as a graft compared to 50% patency rate of a vein graft. Therefore, when planning a CABG, a mammary artery graft is always preferred and is almost always attached to the most important coronary artery, the left anterior descending artery (LAD).
The first stage of CABG is the preparation of the conduits for bypass. This stage includes harvesting the mammary artery (IMA) from the chest wall and harvesting veins from the leg. Surgeons primarily use the conventional method where the chest cavity is opened.
During conventional CABG the surgeon opens the chest by sawing the sternum at the midline. The pleura covering the artery and the lungs is then opened or retracted laterally exposing the IMA. This procedure provides the surgeon with a direct visual of the IMA, while half of the chest is pulled back and elevated with a retractor. Once the IMA is exposed, the surgeon uses electrocautery to divide the artery with its accompanying veins and some tissue as a pedicle or as a single vessel (skeletonized). The IMA side branches are usually divided following the application of a metal clip close to their origin on the artery and cauterization on the chest side. When the artery is divided superiorly up to its origin and inferiorly down to its bifurcation, it is cut at its lower end and at this time its tip is prepared and ready to be attached to the coronary artery that is being bypassed
This traditional technique can be used to harvest each of the mammary arteries, left and/or right. The conventional harvesting procedure takes 15 to 40 minutes. Complications associated with the conventional technique include injury to the vessel itself or to the chest wall. Vessel injuries include bleeding during or following the harvest, direct injury to the artery or thermal injury with decreased flow, while the thermal injury to the chest wall causes sternal wound hypoperfusion with and infection. Any such complications might impede vessel flow and leave it unusable as a conduit for bypass. Furthermore, opening the chest cavity itself is detrimental to the patient, both increasing the risk of the operation and also increasing the recovery time required.
Although minimally invasive techniques are available for harvesting the artery, such as the endoscopic technique which is used as part of the totally endoscopic coronary artery bypass (TECAB) surgery, these techniques have many drawbacks. For example and without limitation, the procedure requires extensive training, it is very time consuming and it requires expensive and specialized equipment. In this method robotic arms are used to harvest the IMA through small incisions on the side of the chest wherein visualization is facilitated by video means. Harvesting using the robotic technique lasts for 60 to 70 minutes. When compared to the conventional technique and despite the cosmetic advantageous, the risk of injury using the robotic technique is higher. The increased risk is primarily due to the limited field of view and limited range of motion of the robotic arms provided by this method. Furthermore, there is also a higher risk of bleeding during the harvest that may require further medical intervention, such as chest opening to control the bleeding.
A well harvested artery obtained with minimal damage to the chest wall has significant effects on postoperative course. As being a major blood supplying artery to the chest wall, there is some compromise of the chest wall blood supply after harvesting the artery and diverting the flow to the heart instead of the chest wall. The combination of this relative hypo-perfusion with surgical intervention serves as a risk for surgical wound infection, a complication that results in high morbidity and mortality rates. This risk is significantly higher in patients with diabetes (40% of CABG patients), who already suffer a microcirculation damage associated with diabetes.